Interpretive Summary: Anthracnose crown rot infects all above-ground parts of the strawberry plant and is severe in strawberry production fields in the southeastern U.S. where the pathogen may spread rapidly during wet harvest seasons, sometimes causing a total crop loss. Fungicides may be used to control anthracnose diseases, but some are no longer effective due to the development of fungicide tolerant strains of the pathogen. Field observations showed strawberry plants grown in soils with low N levels had reduced levels of anthracnose, but their fruit production was also severely reduced. The objectives of these studies were to determine the influence of N, P, and K levels and the influence of N source and concentration on the severity of anthracnose crown rot. It was determined that the source and level of N in fertilizers had a major effect on severity of anthracnose crown rot in strawberry, whereas the level of P and K in fertilizers did not. Plants that received N as calcium nitrate had less severe anthracnose crown rot symptoms than plants that received N in the ammonium form. These trials were conducted using greenhouse grown potted plants, but the results should apply to strawberries grown in very sandy soils such as is typical in Florida. These results suggest that strawberry growers can modify their fertilizer regimes by using calcium nitrate as their N source to reduce anthracnose crown rot severity while maintaining the higher foliar N levels needed to achieve good growth and production. There was a significant difference in foliar N levels among the strawberry clones which suggests that N applications should be tailored to each cultivar; however, the trend of reduced anthracnose severity with nitrate fertilizer was similar on the five strawberry clones in these trials which indicates that other cultivars would respond in the same way. This information may be used by strawberry growers, extension specialists, and other research scientists.

Technical Abstract:
The influence of nitrogen, phosphorus, and potassium on the severity of anthracnose crown rot was evaluated in three greenhouse studies. Strawberry plants were fertilized three times weekly with a modified Hoagland's Nutrient Solution containing the treatments and inoculated eight weeks after treatment applications began with a conidial suspension of the causal pathogen, Colletotrichum fragariae. Disease severity was rated 30 days later on a scale of 0 (no symptoms) to 6 (plant dead). In the first study, the effect of N, P, and K levels was evaluated using 16 treatments: eight N levels with either low P and K or high P and K. Disease severity ratings and percent foliar N increased as N level increased but were not influenced by the level of P and K. In two other experiments, seven N sources were each evaluated at three levels. Plants receiving 160 ppm N had higher disease severity ratings than plants receiving 0 or 40 ppm N. Among plants receiving 160 ppm N, those treated with Ca(NO3)2 had the least disease. When N fertilizer is applied to strawberry plants as Ca(NO3)2, anthracnose crown rot severity should be less severe than when N is applied in ammonium forms.